TROPICAL EXPLOITATION 69 
exploitation has aroused the greatest interest in recent 
times, viz. rubber. Rubber is obtained from many 
different species, but the one that first came into notice, 
the one that as a wild tree produces the greatest amount, 
and the one that is by far the most commonly -culti- 
vated, is the rubber tree of the Amazon valley, the tree 
now usually known as the Parad rubber, Hevea brasi- 
liensis. Other rubber trees of importance occur in 
Africa, in Central America and Mexico, and elsewhere, 
but though exploited commercially for all they are 
worth, they are but little cultivated. 
The Para rubber, growing in the valley of the largest 
river upon earth, a river up which liners of 10,000 tons 
can go for more than 1000 miles, and which has innu- 
merable navigable tributaries, was fortunate in the 
matter of transport. Capital was forthcoming, the 
crop being profitable, and labour in the early days was 
obtained by slavery. A merchant industry thus sprang 
up, with its headquarters at Para. 
This was all that was necessary for a very long period. 
The Indians had known of the properties of rubber 
for a long time, but it was little used in England or 
elsewhere in the colder zones. The real advance in its 
use came with tke discovery of vulcanisation, in which 
by the combination of sulphur with the rubber, its 
nature was changed, and it became much more durable, 
and suited for the manufacture of many different sorts 
of things. From that period onwards, the consumption 
of rubber has increased without any serious break, 
until at the present date it may be looked upon as one 
of the indispensable products for modern civilisation, 
like cotton. 
